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Sensors 2017, 17(9), 2102; doi:10.3390/s17092102

The Impacts of Heating Strategy on Soil Moisture Estimation Using Actively Heated Fiber Optics

1
Water Resources Section, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2600 GA Delft, The Netherlands
2
USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705-2350 USA
3
Dipartimento di Ingegneria Civile, Design, Edilizia e Ambiente, Università della Campania “L. Vanvitelli”, 81031 Aversa, Italy
*
Author to whom correspondence should be addressed.
Received: 27 July 2017 / Revised: 1 September 2017 / Accepted: 7 September 2017 / Published: 13 September 2017
(This article belongs to the Section Physical Sensors)
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Abstract

Several recent studies have highlighted the potential of Actively Heated Fiber Optics (AHFO) for high resolution soil moisture mapping. In AHFO, the soil moisture can be calculated from the cumulative temperature ( T cum ), the maximum temperature ( T max ), or the soil thermal conductivity determined from the cooling phase after heating ( λ ). This study investigates the performance of the T cum , T max and λ methods for different heating strategies, i.e., differences in the duration and input power of the applied heat pulse. The aim is to compare the three approaches and to determine which is best suited to field applications where the power supply is limited. Results show that increasing the input power of the heat pulses makes it easier to differentiate between dry and wet soil conditions, which leads to an improved accuracy. Results suggest that if the power supply is limited, the heating strength is insufficient for the λ method to yield accurate estimates. Generally, the T cum and T max methods have similar accuracy. If the input power is limited, increasing the heat pulse duration can improve the accuracy of the AHFO method for both of these techniques. In particular, extending the heating duration can significantly increase the sensitivity of T cum to soil moisture. Hence, the T cum method is recommended when the input power is limited. Finally, results also show that up to 50% of the cable temperature change during the heat pulse can be attributed to soil background temperature, i.e., soil temperature changed by the net solar radiation. A method is proposed to correct this background temperature change. Without correction, soil moisture information can be completely masked by the background temperature error. View Full-Text
Keywords: active DTS; soil moisture; soil temperature; heating strategy active DTS; soil moisture; soil temperature; heating strategy
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Dong, J.; Agliata, R.; Steele-Dunne, S.; Hoes, O.; Bogaard, T.; Greco, R.; van de Giesen, N. The Impacts of Heating Strategy on Soil Moisture Estimation Using Actively Heated Fiber Optics. Sensors 2017, 17, 2102.

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